Thermionic filament of variable capacity



Feb. 2, 1937. E. F. LOWRY THERMIONIC FILAMENT OF VARIABLE CAPACITY Filed March 15, 1934 INVENTOR finm'zFZah/y 6! ESSES:

ATTORN Y ATENT oFFicE THERMIONIC FILAMENT VARIABLE CAPACITY Erwin F. Lowry, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, 'Pa., a corporation of Pennsylvania Application March 15, 1934, Serial No. 715,644

2 Claims. (01. 25027.5)

UNITED This invention relates to electron discharge de- I have invented a new and useful type of filavices and especially to such a device having a merit for cathode structure for such tubes which cathode of variable capacity. will materially reduce the input power required It is an object of my invention to provide an during that part of the tubes operation when electron discharge device having a main cathode current drains are less than the peak plate cur- 5' section for normal operation of the tube and rent rating. My invention is embodied in the having an auxiliary or booster electron emitting specific form disclosed in the drawing,'but is not portion that will operate when peak current load limited to the specific details disclosed therein.

is necessary in the electrode output circuit. The electron discharge tube I0 comprises the Another object of my invention is to provide usual air-tight envelope H having the anode I2 10 an electron discharge device and circuit therefor and cathode l3 therein. If desired, other elecin which considerable input power is saved by trodes auxiliary to these main electrodes may be having one portion of the cathode operating for placed therein. The cathode structure preferlow output demands and another portion of the ably comprises a section M. This section It has cathode being operated when the demand is at connections 15 and It to terminals I7 and IB to 15 peak load. which a heating means for the cathode can be Other objects of the invention will become more connected. This heating means may, of course, apparent from an examination of the drawing, in be the usual transformer connection l9 to a supply which the figure is a view, partially in crosscircuit of suitable rating.

section and partially diagrammatic, of an elec- The anode l2, which may be of any suitable 20 tron discharge device and its circuit embodying size and shape, has an external connection 20 the invention. connected to the external load circuit 2 I. A suit- In hot cathode tubes of the present art and able input means may be provided such as the especially in gas filled tubes having an oxide circuit 22 through the transformer 23 to this 25 coated cathode, the plate currents which may be external anode circuit. The return anode circuit 25 drawn from the tube are considerably below the lead 28 is connected to a terminal 29 connected thermionic emission of the cathode. This limiin turn to an auxiliary or booster filament por tation is necessary for the reason that the rate tio 24 that is preferably connected to a common of disintegration of the coating material is a point 25 which divides the main filament section 30 function of the space or discharge current denl4 into two portions 26 and 21. 30 sity on the cathode surface. An oxide cathode While my invention in its broadest aspect is not that will operate satisfactorily for 10,000 hours limited to any specific shape or size of the elecat a drain rate of 3 amperes per square inch of trodes, I prefer to make the filament portions in cathode surface has an emission of at least 10 the spiral corrugated ribbon form disclosed in the amperes per square inch of cathode surface. But drawing and more specifically described in my 00- 35 if s Cathode is u at 5 amperes P q a pending application Serial No. 612,505 for a high inch of cathode surface, its useful life may be as efficiency oxide coated cathode method of manulow as 1200 hours. As a result, the filaments for facture filed May 20, 1932. This ribbon is prefe filled tubes are designed to operate at 3 erably formed of the nickel-cobalt iron-titanium amperes per square inch of cathode surface or alloy described therein and is coated with the 40 less in order that the tube may have a satisstandard coating of barium and strontium oxides. factory life. The operation of my device is as follows: The These tubes are operated at much less than tube may be required to have a peak plate curtheir peak rating during a considerable portion rent rating of 5 amperes, for example, but may of their useful life. Quite a number of these only be required to supply acontinuous current of 45 tubes are used in a circuit in which their cathodes 3 amperes or less for the major portion of its life. are heated for over a considerable standby period, The section It is accordingly designed to furnish in order that they may operate for a short time this continuous usual demand of 3 amperes. By at peak load. Other tubes are operated most of designing this filament section I4 and the ourthe time at values much less than their peak load. rent through the transformer I9 to provide these 50 Nevertheless, the filaments must be of such size 3 amperes of current by the electron emission that their peak rating is not to exceed 3 amperes from this main portion I4 of the cathode asper square inch, and this requirement of size sembly, this anode current of 3 amperes or less necessitates a correspondingly large power input returns to the cathode through the auxiliary to operate them at the proper temperature. cathode portion 24. This auxiliary portion 24 has 55 which appreciable electron emission is obtained,

and when 4 amperes is flowing in this external anode circuit, the electron emitting portion 24 will reach full operating temperature of approximately 900 C.

The additional electrons to increase the anode current from 3 amperes to 5 amperes will be,

largely drawn from the auxiliary or booster portion 24 of the cathode assembly, and this additional drain will not adversely aflect the life of the main portion ll of the cathode; This additionaljsupply of electrons is automatically brought into operation by the heating" or the cathode section 24 by the increased anode return current;

'When the external anode circuit decreases its 7 current 'to below 3 amperes, for example, the

auxiliary filament portion 24 will cool and absorb very little of the input energy. Considerable economy will accordingly be effected when the tube is operating below its peak rating or is in a standby position.

V The invention is not limited to filaments for gas filled tubes, but may be found very useful for high vacuum tubes. In gasfilled devices the voltage drop in this type of filament may be limited to about 5 volts, but in high vacuum tubes it may be as much as 2 0 or 25 volts without causing difliculty in operation.

It will be obvious to'those' skilled in the art that many other forms of my invention exist and the only limitations thereon are those necessitated by the prior art or imposed by the following claims. a r a a I claim as my invention: 7

1. A cathode assembly comprising two connections for heating current, electron-emitting portions between said two connections, a connection for return of the anode current and anauxiliary electron-emitting portion between said last-mentioned connection and the first-mentioned electron-emitting portions, the emissivity of the auxiliary portion varying directly in substantial amounts with the anode current.

2. A cathode assembly comprising two electron emitting'portions, one of said portions being electron emitting in response to a heating current provided therefor, the other portion'b'eing electron emitting in response to the load current, the emissivity of said last-mentioned portion varying in substantial amounts with the load current.

ERWIN F. LOWRY. 

